Anterior Approach to Sacroiliac Joint

Revision Sacroiliac Arthrodesis:

• Failed posterior SI fusion with persistent pain and instability
• Anterior column deficiency requiring supplemental anterior fixation
• Pseudarthrosis after posterior-only fusion in high-demand patients

Anterior Pelvic Ring Injuries:

• Unstable anterior pelvic ring injury requiring direct ORIF
• Crescent fracture with anterior SI joint involvement
• Vertical shear injury (APC III, LC III) with anterior SI disruption
• Failed closed reduction of rotational instability

Hardware-Related Issues:

• Prominent anterior SI screws causing nerve compression or vascular compromise
• Removal of broken or misplaced anterior hardware
• Revision fixation after hardware failure

Why Anterior Approach?

• Direct visualization of anterior SI joint and L5 nerve root
• Allows placement of anterior column plate from ilium to sacrum
• Can address anterior soft tissue pathology (scarring, nerve entrapment)
• Necessary for certain revision arthrodesis techniques

Complex Revision Cases:

• Recurrent SI joint dislocation despite posterior fixation
• Need to decompress L5 nerve root (compressed by callus, hardware, or scar)
• Removal of heterotopic ossification around SI joint
• Tumor resection involving anterior SI joint

Primary SI Arthrodesis (Rare):

• Some surgeons advocate anterior approach for primary arthrodesis in select cases
• Allows better visualization of joint preparation
• Theoretical advantage: compression across SI joint from anterior
• However, most surgeons prefer posterior or percutaneous approaches for primary cases

Absolute:

• Active infection overlying surgical field
• Patient medically unfit for prolonged complex pelvic surgery
• Severe adhesions from multiple previous surgeries (relative)

Relative:

• Obesity (BMI more than 40) - extreme difficulty exposing SI joint
• Previous radiation to pelvis (tissue quality poor)
• Osteoporosis (poor screw purchase)
• Pregnancy (relative - avoid if possible)

When to Use Posterior Approach Instead:

• Most primary SI pathology (fusion, fracture fixation)
• Simpler, safer, better bone purchase
• Reserve anterior approach for complex revision cases only

History:

• Previous pelvic surgeries and approaches used
• Mechanism of original injury (if trauma)
• Symptoms: pain location, radiation, neurological symptoms
• Failed treatments (conservative, posterior surgery)
• Functional limitations

Examination:

• Neurological exam CRITICAL:
  • L5 nerve root function (EHL, ankle dorsiflexion, sensation dorsal foot)
  • S1 nerve root function (ankle plantarflexion, sensation sole)
  • Document baseline carefully
• SI joint provocative tests (FABER, Gaenslen, thigh thrust)
• Gait pattern
• Leg length discrepancy (pelvic asymmetry)
• Palpate for prominent hardware anteriorly

EXAM KEY: "The anterior approach to SI joint is HIGH RISK. L5 nerve root injury occurs in 5-15% of cases and causes permanent foot drop. I only use this approach when absolutely necessary after posterior approaches have failed."

Plain Radiographs:

• AP pelvis
• Inlet view (SI joint displacement)
• Outlet view (vertical displacement)
• Lateral sacrum
• Ferguson view (AP with 30-degree cephalad tilt) - best shows SI joint

CT Scan (Essential):

• Fine-cut CT through SI joint (1mm slices)
• 3D reconstruction
• Assess:
  • SI joint morphology and bony anatomy
  • Presence of pseudarthrosis or nonunion
  • Position of previous hardware
  • Bone quality
  • Vascular anatomy (if contrast available)

MRI (Very Helpful):

• Assess soft tissue around SI joint
• Identify scar tissue, nerve entrapment
• Evaluate for infection (high T2 signal, enhancement)
• Look for bone marrow edema (active inflammation)

Vascular Imaging (Consider):

• CT angiography if revision case with extensive scarring
• Identifies aberrant iliac vessel anatomy
• Maps collateral circulation
• Helps plan safe corridor to SI joint

Expected Outcomes:

• Pain relief in 60-80% of revision arthrodesis cases
• Fusion rate: 70-85% with anterior + posterior combined fixation
• Functional improvement variable (depends on chronicity)

Specific Risks (HIGH):

Alternative Treatments:

• Continue conservative management (PT, injections, bracing)
• Repeat posterior approach with bone grafting
• SI joint fusion with percutaneous techniques (iFuse, SI-BONE)
• Pain management referral (chronic pain program)

Type: General anaesthesia (mandatory)

Considerations:

• Prolonged case (2-4 hours typical)
• Muscle relaxation essential
• Arterial line for complex revision cases
• Central venous access if anticipated vascular injury risk high

Adjuncts:

• Tranexamic acid 1g IV at induction
• Broad-spectrum antibiotics (Cefazolin 2g + Gentamicin)
• Cell saver
• Warming blanket

Position: Supine

Setup:

1. Standard supine position on radiolucent table
2. Arms tucked or out on arm boards (surgeon preference)
3. Bump under ipsilateral buttock (15-20 degrees) - improves SI joint access
4. Hip slightly flexed and externally rotated
5. Ensure C-arm can access pelvis from multiple angles
6. Pressure points padded

Preparation:

• Prep from nipples to mid-thigh
• Circumferential prep if iliac crest bone graft needed
• Include entire abdomen (case may extend medially)
• Drape to allow extension of incision if needed

Rate: 5-15% (most common serious complication)

Mechanisms:

• Traction injury from retractors
• Direct laceration
• Thermal injury
• Compression from hardware

Recognition:

• Nerve stimulator shows loss of response
• Visual inspection shows nerve damage
• Post-operative foot drop

Management:

• If recognized intra-operatively:
  • Release all traction immediately
  • Inspect nerve for laceration
  • If lacerated: microsurgical repair (neurosurgery consult)
  • If intact: pad nerve, minimize further trauma
• Post-operative:
  • EMG at 6 weeks
  • AFO for foot drop
  • Physiotherapy
  • Most improve partially over 6-18 months
  • 50% have permanent deficits

Rate: 2-5%

Vessels at Risk:

• Common iliac artery and vein
• Internal iliac vessels
• External iliac vessels

Recognition:

• Sudden hemorrhage
• Expanding hematoma
• Hypotension

Management:

• Immediate:
  • Direct pressure with pack
  • Call vascular surgery immediately
  • Rapid fluid resuscitation
  • Activate massive transfusion protocol if severe
• Definitive:
  • Vascular repair (primary repair if small tear)
  • Interposition graft if large defect
  • Ligation of internal iliac may be necessary (not ideal but life-saving)
  • Post-operative vascular monitoring

Prevention:

• Gentle dissection
• Visualize vessels throughout
• Have vascular surgery on standby for complex revisions

Rate: 1-3%

Structures at Risk:

• L5 nerve root (most common)
• S1 nerve root
• Lumbosacral trunk
• Obturator nerve (if dissection extends too far medially)

Recognition:

• Multiple nerve root deficits
• Severe post-operative pain
• Bladder/bowel dysfunction (if sacral roots involved)

Management:

• Most are traction injuries (neuropraxia)
• Conservative management with observation
• EMG at 6 weeks for prognostication
• Neurosurgical consult if no improvement by 3-6 months

Rate: Less than 1%

Mechanism:

• Adhesions from previous surgery
• Inadvertent perforation during dissection

Recognition:

• Bowel contents or urine in field
• Post-operative peritonitis

Management:

• Intra-operative recognition: primary repair by general surgery
• Post-operative recognition: reoperation, diversion may be needed

Day of Surgery:

• ICU monitoring (high-risk case)
• Neurological checks every 2 hours:
  • L5 function (EHL, ankle dorsiflexion)
  • S1 function (ankle plantarflexion)
  • Document and compare to pre-operative baseline
• Monitor for vascular complications (distal pulses, compartment syndrome)
• Drain output monitoring
• DVT prophylaxis: LMWH from Day 1

Mobilization:

• Bed rest 24-48 hours (allow healing)
• Log roll only
• Avoid hip flexion more than 45 degrees (protects SI joint)

Weight Bearing:

• Toe-touch weight bearing only for 6-8 weeks
• Walker or crutches
• Gradual progression based on pain and X-ray evidence of healing

Restrictions:

• No sitting more than 30 minutes at a time (first 2 weeks)
• No twisting or bending
• No lifting more than 5kg

Wound Care:

• Remove drain when output less than 30ml/day (typically Day 2-4)
• Sutures/staples out at 14-21 days

Imaging:

• X-ray at 2 weeks (AP pelvis, inlet, outlet)
• Check hardware position, alignment

Weight Bearing Progression:

• Week 6: X-ray to assess healing
• If healing progressing: advance to partial weight bearing (50%)
• Week 10-12: Full weight bearing if radiographic fusion evident

Physiotherapy:

• Core strengthening
• Pelvic stabilization exercises
• Gait training
• Avoid impact activities until 6 months

Return to Activities:

• Driving: 8-12 weeks (off narcotics, adequate control)
• Sedentary work: 6-8 weeks
• Manual labor: 4-6 months
• Sports: 6-12 months

Follow-up:

• 6 weeks, 3 months, 6 months, 1 year
• X-rays at each visit
• CT at 6-12 months to confirm fusion

Fusion Assessment:

• Bridging bone across SI joint on CT
• No hardware loosening or breakage
• Clinical: pain-free weight bearing

Outcomes:

• Fusion rate: 70-85% with anterior + posterior combined
• Pain relief: 60-80% in revision cases
• Functional improvement variable
• L5 nerve injury recovery: 50% permanent deficit rate